The present invention generally relates to measurement devices, and more particularly to a measurement device for measuring non-circularity of a generally circular part and providing an indication of non-circularity of the part.
It is often necessary to measure the non-circularity of a generally circular part. This is important because an unacceptable degree of non-circularity of a part can affect how that part couples with other parts or otherwise performs when assembled to other parts.
One present method for determining the degree of non-circularity of a generally circular part is by using calipers to measure the outer diameter of the part or of various structural portions, such as a flange, of a circular part. Using calipers is difficult and does not always provide the degree of accuracy desired. Also, circular parts of significantly varying diameters may require the use of different calipers, which further introduces inconsistencies into the circularity measuring process.
One particular type of gauge used for determining the out-of-roundness of a circular part is a slide gauge. The slide gauge typically consists of a graduated member with a fixed jaw and a sliding member also with a jaw. However, these types of gauges suffer from various limitations due to the construction of the jaws typically used, which can limit the variation in diameter of the parts which can be checked.
Another method for measuring out-of-roundness involves making a diameter measurement through a common, cross-sectional plane, such as those made by a micrometer, bore gauge or comparator stand. These two-point measurement methods are not considered to yield especially accurate out-of-roundness values. This method is typically used in comparison tests where functional or performance criteria have been related to geometric conditions based on a particular roundness measurement.
Yet another method for measuring out-of-roundness is by evaluating a typical cross-sectional profile of a part in terms of its radial deviations from a defined center of the part. This method typically involves the use of a stylus which is placed in contact with the part surface, for example, a horizontal lathe roundness measurement tool. An appropriate stylus force is used to maintain adequate contact with the part surface. The force used depends on the hardness, flexibility, and the maximum compressive strength of the part material itself, as well as the rotational speed and mass of the stylus assembly and the stylus tip radius.
Still another method for measuring out-of-roundness involves the use of a V-shaped block which receives the part to be measured. A stylus is used to then make out-of-roundness measurements with the part.
Still further forms of out-of-roundness measuring involve image processing techniques where an image of the part is made, electronically processed, and quantified using image processing algorithms. Proprietary gauges are also used which rely on multiple cord measurements of a part. Adjustable screw engages have been used in which the part being checked is placed inside of a ring and the diameter of a part is measured relative to the inner diameter of the ring.
All of the above methods have limitations relating to either accuracy or the complexity of the tool required to perform the out-of-roundness measurement. Therefore, the need exists for a relatively simple, accurate, out-of-roundness detection tool that can be used with generally circular parts having a wide variety of diameters which accurately indicate a degree of out-of-roundness of a circular part.
The present invention is directed to a measurement device and method for detecting the out-of-roundness of a circular part or work piece. The apparatus comprises a base assembly having an elongated channel formed therein. A travel or follower assembly providing a constant part contact force is operatively coupled in the channel, and also operatively coupled to a recirculating ball bearing and rail assembly which operates to move the travel assembly along the elongated channel. A measurement device is also operatively coupled to the travel assembly and provides a measurement indication depending upon movement of the travel assembly.
To test the circularity or out-of-roundness of a circular part, the part is placed within a corner of the base. The travel assembly is abutted against a surface of the circular part and the part is then rotated. The greater the degree of out-of-roundness of the circular part, the greater the degree of movement of the travel assembly. This movement is detected by the measurement device which provides an indication of the out-of-roundness to a user.
In one preferred form, the base includes a 90-degree corner portion within which the circular part is placed. The base also includes an elongated channel formed therein within which a portion of the travel assembly moves slidably. The apparatus is relatively simple and inexpensive to construct and can accommodate parts having a considerable variation in diameter.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the invention.